The proposed experiments will investigate the regulation of food intake in humans. Two hypotheses will be tested. The first is that the regulation of the intake of dietary fat differs from that of carbohydrate. The second hypothesis is that the regulation of these nutrients differs between normal weight non-dieting subjects, and obese and normal weight dieters. These hypotheses will be tested in a series of experiments that systematically introduce variable which increasingly approximate normal feeding situations. The following experiments are proposed: 1) Differences in the time course of the inhibitory effects of fats and carbohydrates on subsequent ingestion will be determined in a highly controlled test in which the preload and subsequent test meal are similar. 2) The degree to which subjects detect and compensate for varying levels of fat and carbohydrate will be determined by systematically varying the number of calories in fixed volume preloads with similar sensory properties. The test meal will again be similar to the preload. 3) The regulation following different levels of fat and carbohydrate in preloads will then be assessed in more natural situations, in which the test meal following the preload provides a choice of luncheon foods. Twenty-five day studies in a residential laboratory will extend these findings to determine the long-term adjustments in response to alterations in calories from fats or carbohydrates in a normal lunch. This progression of studies from the highly controlled to the more natural feeding situation will allow us to determine how factors such as variety, palatability, and differences in the physiological management of nutrients contribute to control of food intake. Differences in response to nutrient and caloric manipulations between obese subjects and normal weight dieters and non-dieters will allow suggestions for rational treatments of obesity.